Two-sided hydraulic system



May 12, 1964 c. G. HAcKENBr-:RGER 3,132,622 I TWO-SIDED HYDRAULIC SYSTEM MTM ATTORNEYS May 12 1964 c. cs. HACKENBERGER 3,132,622

Two-SIDED HYDRAULIC SYSTEM 5 Sheets-Sheet 2 Filed NOV. 8, 1961 W l r-a l ciad INVENToR. c.G.HAcKENBe/?GER ATTORNEYS May 12 1964 c. G. HACKENBER'GER 3,132,622

Twos1nED HYDRAULIC SYSTEM z5 'T1 INVENTOR.

c. G. HncKE/veese R ATTORNEYS c. G. HACKENBERGER 3,132,622

TWO-SIDED HYDRAULIC SYSTEM May l2, 1964 5 Sheets-Sheet 5 Filed Nov. 8. 1961 ATTORNEYS United States Patent Olice 3,l32,622 Patented May l2, i964 3,132,622 TWO-SEDEDHYDRAUMC SYSTEM Claus Guenther lltlackenberger, Tacoma, Wash., assigner to Tacema ilscathuilding Co., Enc., Tacoma, Wash., a corporation of Washington Filed Nov. il, 196i, Ser. No. 150,970 '7 Claims. (Cl. 11A-235) This invention relates to two-:sided hydraulic systems, `and namely systems in which each of several pieces of lhydraulically powered equipment on one side ofthe system nds a functioning counterpart on the other side of the system. Particularly lending itself to the employment of the teachings of the present invention is fa minesweeper equipped with identical deck machinery for the port and starboard sides of the vessel.

For its principal object the invention aims to provide a hydraulic system of the described nature in which each of the two sides is Ia seltf-suflicient system with power derived from its own engine-driven hydraulic pumps but which may, at will of the operator, draw for its power upon the power source of the other side of the system.

Pls a further tand important object the invention aims to provide a hydraulic system of the described nature in which the hydraulic pumps are continuously driven and embodying a pilot circuit through which the hydraulic oi-l is circulated at a comparatively low pressure during periods when none of the deck machinery is being operated, hence reducing the amount of power required by the pumps from the engines during such periods, and accomplishing the ancillary end of preventing excessive heatingof the hydraulic oil, as would occur were the oil required to pass a relief valve at high pressure.

A yet `additional object of `the invention is to provide *a hydraulic system incorporating a means which automatically protects the hydraulically driven motors against overload.

With the above objects and advantages in view, and further aiming to provide a hydraulic system embodying means protecting the motors against either surge or cavitation when the control valve is shut off, the invention consists in the novel construction Iand in the adaptation and combination of parts hereinafter described and claimed.

ln the accompanying drawings:

FIGURES l through 5 are diagrammatic illustrations which, taken together, portray a two-sided hydraulic system constructed to embody preferred teachings of the present invention.

FIG. 6 -is a master view giving the key to the location of such FIGS. l through 5.

While applicable to sundry hydraulically activated equipment, the teachings of the present invention yare thought to be best exemplied as applied to a minesweeper, and it is this lapplication to which the description will be expressly directed.

To perform :the necessary functions of a minesweeping Vessel, it is required that means be provided for taking and paying out the cable for the minesweep,` for reeling in and paying ont both magnetic cable and acoustic cable, and for hoisting and lowering, to Iand from the ve'ssels deck, the floats which are employed to carry the minesweep cable laterally from the vessel. For the take-in and pay-out functions respective deck Winches are provided for the acoustic cable and for the magnetic cable, 'with one located to starboard and the other to port, and separate deck Winches are also provided for each of the two cables which sweep `the waters which lie to the opposite sides of the vessel. Separate cranes carried upon the Vdeck at the stern ofthe vessel perform the hoist and lowering work, and these are likewise located one at the port and the other at the starboard side.

According to the present invention the power for the operation of the described deck machinery is hydnaulic. The pumps from which said power originates are mounted below-decks in two pairs, one said pair for powering the starboard deck machinery units and the other for powering the port deck machinery units. The ship carries two service generators, and each of these generators drives a respective one of the two pairs. The two pumps of each pair are unmatched, with each said pump supplying a separate subcircuit, as it were. The starboard stern :crane and the starboard minesweep winch are powered from one of these subcircuits, and the starboard cable reel from the other. Similarly, the two subcircuits associated with the other or port pair of pumps handle the port deck machinery. Through a cross-over arrangement which will 'later be described, the port pair of pumps can be made to power the starboard deck machinery, and the starboard pair of pumps the port deck machinery.

Each said hydraulic subcincuit is divided Iinto a power circuit and a connecting pilot circuit, with the latter constituting, in effect, the nervous system of the hydraulic installation. The arrangement is one in which hydraulic oil constantly circulates through the pilot lines under conditions when the manual control valves of the concerned subcircuits are in neutral or stop positions. The circulating oil is at low pressure with the llow uninhibited tbetween the pump and a point of dump leading back to the supply tank. Upon actuation of any control valve the related pilot line ow is interrupted. A main relief valve, responding to the rise of pressure, shuts off the open route to the supply tank and the pumped oil is directed through the power line to the actuated control valve and thence to the motor of the concerned piece of deck machinery.

lt is believed that the above introductory outline will add to an understanding of the system which will be now described with reference to the drawings.

Designated by the numerals l2, 13 are the two pumps, each ixed displacement, which draw from a supply tank l@ and deliver hydraulic Huid to the two subcircuits of the vessels starboard deck machinery. The corresponding pumps for the port side lare designated by 112 and ylllt. inasmuch as deck parts are identical for the two sides of the vessel, `a description of one side will sultice for the other, with reference being made only to cross Iconnections which are provided between the port and the starboard systems of huid-flow pipes. As with the mentioned pumps, port side counterparts of the starboard side components will be identified by like ordinals prefixed by the ordinal 1.

The starboard cable reel and the minesweep winch are each powered by a respective rotary motor of xed displacement, as ll and 23, reversible for reeling in or paying out cable. The stern crane, by contrast, admits of being luifed and trained as well as performing its basic hoist function, and for these three offices employs, in the respective instance, a double acting piston-cylinder motor 32, a reversible rotary motor 3l, and a reversible rotary motor 30. There is also incorporated, compleinenting such motor 3d, a single-acting piston-cylinder motor 3S having as its function to release a spring-set brake in concert with the motivation of the motor 3l).

Associated with each of said motors 17, 23, 32, 31 and 30 is a respective manually operated four-way control valve, as 16, 22, 28, 27 and 26. While essentially threepositioned, these valves are all designed to provide speed regulation, being particularly sensitive at very low speeds where inching is required. All main ports are blocked in the neutral or stop position so as to establish a alaaesa hydraulic lock. The control valves are identical except for pipe connection sizes and the use of auxiliary ports. Valve 26 controls the brake-releasing cylinder 3S in addition to the motor 3l) and makes use of all auxiliary ports. Unused ports in the other control valves are plugged. Each said control valve has two integral spools, one for directional control of the concerned hydraulic motor and the other to block olf a normally open passage through which the hydraulic Huid of the pilot circuit flows.

Reverting to the pumps 12 and 13, pump 12 has the lower capacity and handles only the cable reel. The larger-capacity pump 13 handles the minesweep winch and the stern crane, albeit no call arises for the activation of both at the same time. From pump 12 pressure fluid feeds by connecting lines 51 and 52 to one of two front-side ports of the valve 15, and fitted in these lines is a check valve S9 and a normally open safety or damagecontrol valve 41. Upstream from the check valve, and which is to say between such valve and the pump 12, a flow line 7@ leads to a main relief valve 1li. This valve automatically creates a passageway between pressure lines and the supply tank and is a piloted valve having its minimum pressure established by a spring. An oriiiced passage is provided from the pressure port into the spring pocket, commonly referred to as the control chamber. A passageway connects the control chamber to a pilot valve. This pilot valve normally allows unrestricted flow of a small quantity of oil through the systems pilot circuit, in which circumstance the main spool of the relief valve opens and dumps to the supply tank at the comparatively low-level pressure of 50-75 p.s.i. Should the pilot circuit become closed, subjecting the pilot valve to high pressure, added hydraulic pressure is applied to the control chamber and holds the main spool closed until the high-level relief valve setting is reached. Should the pressure exceed this high setting the main spool opens and empties to the tank as protection to the system. A suitable main relief valve for my purpose is manufactured by Double A Products Co., Manchester, Michigan, Model BTF-185-K508, with a maximum operating pressure of 3000 p.s.i. The dump from said valve is indicated in the drawing by 71, and the flow line connecting with the pilot circuit by 61.

Connecting with the two sides of the motor 17 are flow lines 53 and 55, with the former leading directly to one of two back-side ports of the control valve 16 and the latter leading to a counter-balance valve 13 and thence by line 57 with the other back-side port. The counterbalance valve allows free ilow of pressure oil to the motor 17 in the direction necessary for hauling in cable (namely from said second port to the motor). It prevents reverse flow excepting where the pressure of the supplied oil exceeds a given setting, say 260 p.s.i. Considering said counter-balance valve as it is represented in FIG. 4, pressure uid supplied to line '7 can ow freely through the check valve, line 55, the reversible motor 17, and line 53. This is the haul in direction of rotation of the motor, which perforce means that the motor is under constant load and hence not subject to an over-running action. When the motor turns in the opposite or pay-ou direction, it is not pulling a load and hence would be subject to over-running in the absence of the counter-balance valve. The path of travel of the oil when it turns the motor in this opposite or pay-out direction is from line 53 through motor 17, thence through line 55 to the by-pass spool (shown by a feathered blade) of the valve 18. A spring (shown between the check-valve and the spool) normally holds the spool in a flow-blocking position. The spool can move to an open position only when the pressure of the spring is overcome by a countering pressure of superior intensity, stated above as being 260 p.s.i. This countering pressure is passed to the valve 18 through a pilot line 58 and develops as back-pressure occurs in line 55. When the spool blocks the flow of oil upon delivery of pressure oil to line 53, the motor starts to turn in a pay-out direction in that there is an instant rise of back-pressure to the intensity necessary to shift the spool to open position against the yieldingly resistant pressure of the spring. Upon such shift the back-pressure drops o and the spring takes over to return the spool toward its owblocking position, whereupon the pressure again builds up to again shift the spool to its oil-flow position, which permits pressure oil to again ow through the motor to turn the same. The spool is in a constant shuttling condition but the rise and fall of pressure is so rapid that the mean result is a levelling out and a more or less continuous, albeit controlled, flow of oil turning the motor in its pay-out direction. Over-running cannot occur in that the spring instantly shifts the spool toward an oil-blocking condition when back-pressure drops. Between lines 53 and S5 there is introduced a dual relief valve 20 to protect motor 17 from excessively high pressure surges, the result of inertia loads which are caused by a sudden shut-oif of valve 16 and resulting high pressure in consequence of rapid acceleration or deceleration of the reel. The other of the afore-mentioned two frontside ports of the control valve 16 is a dump opening returning, as at 54, to the supply tank 1i?. The normally open pilot spool, hereinabove referred to, related to and made integral with the pressure spool of the control valve 1d, has its front-side port connecting by pipe 62 with the pilot line 61. From its back-side port, connecting pipes 63 and 643- lead to the starboard-side port of one of four integral spools of a manually operated and normally closed cross-over valve 40. In this normal condition of the cross-over valve said one spool provides communication from the pilot pipe 64'. to a dump port 65 for returning the hydraulic fluid to the supply tank.

Proceeding now to the other sub-circuit of the starboard deck machinerys hydraulic system a main supply line 7273-75S19tl leads from pump 13, being likewise iitted with a check-valve 59 and a normally open in-line safety valve 41, and similarly connecting, upstream from the check-valve, with a main relief valve 21 identical with the relief valve 14. Branching off said main supply line are lines 76, 82, 91 and 96 leading in each instance to one of two front-side ports of a respective one of the control valves 2?., 26, Z7 and 28. The other front-side port is a dump opening connecting in each instance, as at 311, 8d, 9S and 99, with a return line leading to the supply tank 1t).

The components of the hydraulic circuits for the individual motors 23, 30, 31 and 32 each reliect the function which the motor performs. Thus the components for the motors 23 and 30, both of which drive a cable-winding drum, are identical with those for the cable-reel motor 17 with one addition, and that is the provision, for the crane hoist drum shaft, of the referred-to brake which is made automatic in that it is spring set and released by action of the hydraulic cylinder 35. The counterbalance and dual relief valves for the motor 23 are designated by 24 and 25, respectively, those for the motor 3@ by 33 and 34. In the instance of the crane-training motor 31, and the crane-lufling cylinder 32, both could be subject to overloading in either direction of travel and there are accordingly provided counterbalance valves blocking free discharge of hydraulic fluid in both such directions. For the motor 31, such valves are each designated by 36 and the pilot connections therefor by 83 and 84. A dual-relief valve is shown at 37. For the cylinder 32, the two counter-balance valves are each designated by 38 and their pilot connections by 93 and 94. S9 represents a flow control valve set, say, for 8 gpm.

The pilot function of the main relief valve 21 is imposed upon the last-described sub-circuit by hooking the pilot spools of the several control valves 22, 26, 2.7 and 28 in a series circuit so that the act of blocking off pilot ilow through any such valve will establish in the control chamber of the main relief valve the high pressure necessary to close the dump route to the supply tank and responsively raise the oil pressure within the supply line 72-73--75-81--90 to a high working level. Accordingly, pipe 68 leads from pilot line 67 to the front-side port of the pilot spool of valve 22, and pipe 69 leads from the back-side port of such spool to the frontside port of the pilot spool of valve 26. The pilot spools of valves 27 and 28 are connected in turn by pipes 77 and 78, and the line thence connects by pipes 79 and 92 with a starboard-side port of a second of the four integral spools of the cross-over valve 40. This and the previously described pilot spool are denoted by 40a and 40b, respectively. As with the latter spool such spool 40a, in the illustrated normal position of the cross-over valve, establishes communication from the pilot pipe 92 to a port 98 dumping to the supply tank. It should be here noted that pipes 64 and 92 which comprise the downstream ends of the two starboard pilot circuits each similarly constitute downstream ends for the port pilot circuits. Pipes 163 and 179 provide the cross connections therefor.

The cross-over valve is a three-position valve with two ports on each side of each pilot spool. ln addition to the described connections with pipes 64 and 92 and with the dumps 65 and 98, each side connects, as by pipes 66, 97, 166 and 197, with upstream ends of the related pilot circuit.

The other two spools of the cross-over Valve are denoted by 40c and 40d. Each is a two-way valve connecting in one instance with pipes 74 and lt''lil branching from the main-line pipes 73 and 173, and in the other instance with pipes 60 and 160 branching from the main-line pipes 52 and 152. In the neutral position, pipe 74 is isolated from 174, and pipe 60 is `isolated from pipe 168. Shifted to the right end limit of travel, communication becomes established from starboard-side ports to portsideports of the spools; Shifted to the left end limit of travel, communication becomes established from portside ports to starboard-side ports of the spools.

Reverting to the 4-way spools 40a and 4Gb, movement of the cross-over valve in the former direction from neutral brings the pilot pipes `166 and 197 into communication with the dumps 65 and 98 and blocks off thetwo starboard pilot circuits. Working pressure thus becomes established from pumps 12 and 13 on pipes 52 and 73 and through the crossover connections to the portside motors. Movement of the cross-over valve to the left similarly blocks the port pilot circuits while dumping from the starboard pilot circuits, and working pressure of the pumps `112 and 113 is made available to the starboard deck machinery. i

Tracing the operation, the ships service generators are started and clutched to the pumps, which draw oil through tilters from the reservoir and disperse the oil, under pressure, into the four supply circuits. Power is now available to the operators of the deck machinery. The pilot circuits are actually the nervous system. When all of the manual control valves are in neutral position the pilot circuit for any given supply circuit is a complete circulating system, but when a control valve is actuated to operate a hydraulic motor in either of its two directions of rotation the pilot iiow becomes interrupted, whereupon a rise of pressure occurs between the control valve and the related main relief valve which has been dumping oil back into the reservoir. This pressure rise causes the main relief valve to shut off the dump route, whereupon working pressure is instantly "established in the supply circuit. When the control valve is again placed in neutral, interrupting flow to the concerned motor, pumped hydraulic liuid is again rerouted to the reservoir.

The reaction of the systems to the operation of any piece of deck machinery is the same with the exception of the crane hoist. This unit has the unique feature of having its hoist drum shaft equipped with a spring-set hydraulically released brake.

Should an occasion arise where a pump is out of service, the cross connection allows the pump for the deck machinery of the vessels other side to be substituted.

Considering the operation of any given motor, with the minesweep winch taken as an example and assuming that cable is being paid out, there would be a tendency for the external load to run away with the cable causing the hydraulic motor 23 to rotate ever faster, operating as a pump instead of a motor. An automatic counterbalance valve (the valve 24) `is installed to prevent this condition, having the eiiect of blocking the motor discharge lines until the pressure in the payout supply line reaches about 250 p.s.i. After the desired amount of cable has been let oil the drum, and when the operator shifts the control valve to the stop position, the masses of rotating equipment in the winch assembly and the reducer unit will have the effect of putting an excessive inertia load on the motor. This source of possible damage is eliminated by the installation of the dual relief valve (the valve 25) which compensates for the added pressure by opening (at 2300 psi.) a route to the return line and allowing the hydraulic oil to escape from the supply system.

It is believed that the invention will have been clearly understood from the foregoing detailed description of my now-preferred illustrated embodiment of the invention. Changes can be resorted to Without departing from the spiriti of the invention and it is accordingly my intention that no limitations be implied and that the hereto annexed claims be given the broadest interpretation to which the employed language fairly admits.

Wh at l claim is:

l. In a hydraulic system, in combination: two separate sides each equipped with at least two hydraulic motors, a respective control valve for each motor, an oil reservoir, a respective power-driven pump for each side drawing oil from the reservoir and feeding same to a respective supply line leading by separate branches to the several valves of the related side, a respective pilot line supplied with oil from said supply lines, separate connections both from said pilot lines and from the supply lines each dumping to the reservoir, means acting automatically to open said pilot line dump connections only when all of said control valves of a related side are closed and to close said pilot line dump connections when any one of the related control valves are open, means made responsive to said opening and closing of the pilot line dump connections acting automatically in the respective instance for opening and closing the related supply line dump connection, the closing of said supply line dump connections establishing a high-pressure working condition in the related supply line, and a valved crossover connection joining the two sides of the system, the valve in said cross-over connection being a S-position control valve acting, when occupying a normal centered position, to isolate both the supply line and the pilot line for one of said sides from the supply line and the pilot line for the other side, and acting, when moved in opposite directions from center, to in one instance connect the supply line of one side to the supply line of the other side while bringing the pilot line of the latter side into functioning association with the supply line of the first said side, and in the other instance to connect the supply line of said other side to the supply line of the first said side while bringing the pilot line of the rst said side into association with the supply line of such other side.

2. In a hydraulic system, in combination: two separate sides comprised, in each instance, of a reversible hydraulic motor, a 3-position 4-Way control valve, a respective connection from each of two back-side ports of the valve one to one and the other to the `other of the two sides of the motor, at least one of said connections having a counterbalance valve iitted therein permitting free flow of.` hydraulic fluid through `said connection directively toward the motor but allowing hydraulic fluid to flow through said connection directively from the motor only upon the development of a predetermined high pressure in the other of the two connections, an oil reservoir, a dump connection from one of two front-side ports of the valve to the reservoir, a power-driven pump drawing oil from the reservoir and feeding same to a supply line leading to the other of the two front-side ports of the control Valve, a pilot line fed with oil from said supply line, separate valvcd connections both from the pilot line and from the supply line each dumping to the reservoir, means acting automatically in response to a closing and an opening, respectively, of the control valve for opening and ciosing the valve in the pilot line dump connection, and means made responsive to said opening and closing of the pilot line dump connection acting automatically to open and close the valve in the supply line dump connection, the closing of said supply line dump connection establishing a high-pressure working condition in the supply line; and a valved cross-over connection joining the two sides of the system, the valve in said cross-over connection being a 3-position control valve acting, when occupying a normal centered position, to isolate both the suppiy line and the pilot line for one of said sides from the supply line and the pilot line for the other side, and acting, when moved in opposite directions from center, to in one instance connect the supply line `of one side to the supply line of the other side while bringing the pilot line of the latter side into functioning association with the supply line of the rst said side, and in the other instance to connect the supply line of said other side to the supply line of the first said side while bringing the pilot line of the first said side into functioning association with the supply line of such other side.

3. A hydraulic system according to claim 2 characterized in that there are a plurality of such motors for each of the two sides provided in each instance with a respective said control valve each fed from the supply line of the concerned side by a respective branch connection, the means which closes the valve in the pilot line dump connection of either said side responding to an opening of any of the control valves of said side.

4. In a minesweeper, in combination: sets of reversible hydraulic motors one set for powering port and the other set for powering starboard deck machinery, a respective 4-way 3-position valve spool controlling each of said motors connected by the two back-side ports with the two sides of the related motor, the spool blocking communication between front and back-side ports when occupying a centered position and establishing communication when moved in either direction from center, an oil reservoir, respective power-driven pumps drawing oil from the reservoir and feeding one to the head end of a supply circuit for the port motors and one to the head end of a supply circuit for the starboard motors, a respective 2-way 3- position valve spool movable in unison with each of said 4-way spools, the spool establishing communication between front and back-side ports when occupying a centered position and blocking communication when moved in either direction from center, a main relief valve for each of said supply circuits having its control chamber direct-connected to the head end of the related said circuit, a pilot circuit for each of said supply circuits connected by its head end to the related control chamber and dumping from its tail end to the reservoir and between said head and dump connections coupling the several 2-way spools of the related set of deck machinery in a series circuit, a normally open dump connection from the control chamber of each of said main relief valves to the reservoir closed automatically by a pressure rise reflecting a blocking of the related pilot circuit, respective branch connections from each supply circuit to a respective one of the front-side ports of each of the 4- way spools of the related set of deck machinery, the other or" the two front-side ports of each of said 4-Way spools being a dump connection leading to the reservoir, and a cross-over control valve movable in either direction from a normally closed centered position which isolates both the supply circuit and the pilot circuit related to one set of deck machinery from the supply circuit and the pilot circuit related to the other set of deck machinery and acting, when moved in one direction from center, to crossconnect the supply circuit related to one said set with that of the other while bringing the pilot circuit of the latter set into functioning association with the supply circuit of the former set and, when moved in the other direction from center, to cross-connect the supply circuit related to such other set with that of the former set while similarly bringing the pilot circuit of such former set into functioning association with the supply circuit of such other set.

5. The minesweeper recited in claim 4 in which the recited sets of motors handle a respective minesweeping winch and a respective stern crane, and having a respective second hydraulic system for both the port and the starboard sides `of the vessel of which the components are identical with the recited components of the first said systems and which connect, port system and starboard system, by a similar cross-over valve, the two crossover valves being connected so as to work in concert, but the iirst and second said systems for a corresponding side of the vessel, port or starboard as the case may be, being otherwise independent of one another.

6. A minesweeper according to claim 5, a plurality of said motors being provided for each stern crane one to perform a hoist function, one to perform a training function, and one to perform a lufling function, and having a spring-set brake associated with the hoist motor released hydrauiically in concert with imposition of hydraulic pressure upon the hoist motor.

7. A hydraulic system according to claim 2, said motors each having a relief valve associated therewith protecting the motor against an excessive inertia load.

References Cited in the le of this patent UNITED STATES PATENTS 2,103,530 Henry Dec. 28, 1937 2,319,551 Linden et al May 18, 1943 2,775,429 Ashton Dec. 25, 1956 2,805,781 Senn Sept. 10, 1957 3,071,926 Olson et al Jan. 8, 1963 

1. IN A HYDRAULIC SYSTEM, IN COMBINATION: TWO SEPARATE SIDES EACH EQUIPPED WITH AT LEAST TWO HYDRAULIC MOTORS, A RESPECTIVE CONTROL VALVE FOR EACH MOTOR, AN OIL RESERVOIR, A RESPECTIVE POWER-DRIVEN PUMP FOR EACH SIDE DRAWING OIL FROM THE RESERVOIR AND FEEDING SAME TO A RESPECTIVE SUPPLY LINE LEADING BY SEPARATE BRANCHES TO THE SEVERAL VALVES OF THE RELATED SIDE, A RESPECTIVE PILOT LINE SUPPLIED WITH OIL FROM SAID SUPPLY LINES, SEPARATE CONNECTIONS BOTH FROM SAID PILOT LINES AND FROM THE SUPPLY LINES EACH DUMPING TO THE RESERVOIR, MEANS ACTING AUTOMATICALLY TO OPEN SAID PILOT LINE DUMP CONNECTIONS ONLY WHEN ALL OF SAID CONTROL VALVES OF A RELATED SIDE ARE CLOSED AND TO CLOSE SAID PILOT LINE DUMP CONNECTIONS WHEN ANY ONE OF THE RELATED CONTROL VALVES ARE OPEN, MEANS MADE RESPONSIVE TO SAID OPENING AND CLOSING OF THE PILOT LINE DUMP CONNECTIONS ACTING AUTOMATICALLY IN THE RESPECTIVE INSTANCE FOR OPENING AND CLOSING THE RELATED SUPPLY LINE DUMP CONNECTIONS, THE CLOSING OF SAID SUPPLY LINE DUMP CONNECTIONS ESTABLISHING A HIGH-PRESSURE WORKING CONDITION IN THE RELATED SUPPLY LINE, AND A VALVED CROSSOVER CONNECTION JOINING THE TWO SIDES OF THE SYSTEM, THE VALVE IN SAID CROSS-OVER CONNECTION BEING A 3-POSITION CONTROL VALVE ACTING, WHEN OCCUPYING A NORMAL CENTERED POSITION, TO ISOLATE BOTH THE SUPPLY LINE AND THE PILOT LINE FOR ONE OF SAID SIDES FROM THE SUPPLY LINE AND THE PILOT LINE FOR THE OTHER SIDE, AND ACTING, WHEN MOVED IN OPPOSITE DIRECTIONS FROM CENTER, TO IN ONE INSTANCE CONNECT THE SUPPLY LINE OF ONE SIDE TO THE SUPPLY LINE OF THE OTHER SIDE WHILE BRINGING THE PILOT LINE OF THE LATTER SIDE INTO FUNCTIONING ASSOCIATION WITH THE SUPPLY LINE OF THE FIRST SAID SIDE, AND IN THE OTHER INSTANCE TO CONNECT THE SUPPLY LINE OF SAID OTHER SIDE TO THE SUPPLY LINE OF THE FIRST SAID SIDE WHILE BRINGING THE PILOT LINE OF THE FIRST SAID SIDE INTO ASSOCIATION WITH THE SUPPLY LINE OF SUCH OTHER SIDE. 